The present invention relates to a device for the controlled release of an active agent to a host. In particular, the present invention relates to transdermal delivery patches that are laminates having a cellular foam layer containing an active agent. More particularly, the present invention relates to transdermal devices for the topical application of active agents such as nicotine.
Transdermal administration systems are well-known in the art. Occlusive transdermal patches for the administration of an active agent to the skin or mucosa are described in U.S. Pat. Nos. 4,573,996, 4,597,961 and 4,839,174.
One type of transdermal patch for the administration of an active agent is disclosed in U.S. Pat. No. 5,016,652. In this case, an absorbant pad is covered on its upper surface by an occlusive layer, with the lower surface coated with an adhesive to affix the pad to the skin. The pad is disclosed as being a somewhat absorbant material capable of functioning as a reservoir, and is formed of a cotton, non-woven or similar cloth-like material capable of retaining, but yet dispensing, a liquid carrier. The pad may also be formed of a silicone polymer matrix of a cross-linked silicon rubber and having micro-sealed compartments which are effectively formed by the in situ cross-linking of the silicon rubber. The efficient production of patches having uniform transdermal release rates and other desirable properties is problematic with patches of this type, particularly when the pad is formed of cotton, non-woven or a cloth-like material.
Another type of transdermal patch for the administration of an active agent is disclosed in U.S. Pat. No. 4,597,961. In this case, a patch is disclosed in which an occlusive backing is formed having a cavity, located within which is a suitable absorbant material, such as a sponge, non-woven or cotton. The occlusive layer extends peripherally beyond the cavity and the peripheral area is coated with an adhesive for affixing the patch to the skin. Cotton and sponge reservoirs are undesirable because they possess non-uniform rate of release. Again, the efficient production of patches of this type having a uniform and consistent release rate is problematic.
There remains a need for improved transdermal patches having absorbant layers that function as carriers for active agents. A transdermal patch having this structure that can be produced efficiently with little variation in release rate and other transdermal properties from patch to patch would be highly desirable.